The MKP-type capacitors consist of a low-loss dielectric formed by pure polypropylene foil. A thin self-healing healing mixture of zinc and aluminium is metallised directly on one side of the PP-foil under vacuum. This ensures long operating life of the capacitor. In some cases additional unmetallised foils are added between the metallised ones. The capacitor elements are dried in a vacuum. After insertion into the capacitor case, a patented viscous polyurethane resin, mainly containing castor oil, is introduced. This protects the winding from environmental influence and provides an extended life expectancy and stable capacitance. Like the MPP-dielectric, MKP is self-healing.

Paper in Oil Capacitors Audio Consulting.

Paper in oil capacitors are commonly used in high-end tube amplifiers and sound systems. They also have uses in speaker crossovers. Used in tube amps for power supply filtering, or as AC interstage coupling elements, or in passive loudspeaker crossovers, they give stunning results when compared to audio grade polymer film or other paper in oil capacitors. Wherever you may use them, they make you realise the amount of dielectric noise plastic film capacitors can produce.

Moreover, as they are designed for 0% failure under tropical conditions, the capacitors meet the highest expectations when it comes to stability and very long term performance in very high quality audio equipment.

There are different types of paper in oil capacitors, The second is Kristall Cap, designed to provide the best performance possible!
If money isn't important, 10 uF / 1600 VDC Kristall Cap will cost you $495- Australian

Jensen Paper in Oil capacitors

You should also check Jensen caps as they are among the best you will find anywhere. Their pure metal foil Paper-in-Oil capacitors are used world wide by DIY audiophiles and high-end amplifier manufacturers.

I would recomand Google search.. You'll find just about anything that might be of interest to you..

MKP is the polypropilene dielectric cap
You can by them new in almost every store...They are sonicly good but have limits in a values hard to find more the 20
miro F and higher Voltage values...
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oil caps are old parts
using in tube amps for the Power supplys
as well as for the signal flow
I used them even for the some crossover
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out of production i thik
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(Be careful That oil inside is extremly
dangerous causing cancer etc...)